As a technique for imparting water and oil repellency to the surface at the same time, it has been common to treat an object with an organic solvent solution or an aqueous dispersion of a copolymer containing polymerized units of a polymerizable monomer containing a polyfluoroalkyl group (hereinafter, a polyfluoroalkyl group will be referred to as an Rf group) in its molecule or a copolymer of such a polymerizable monomer with another monomer (hereinafter such a copolymer may be referred to also as an Rf group-containing polymer).
The development of such water and oil repellency is attributed to formation of “a low energy surface” having a low critical surface tension on the surface of a coating film by surface orientation of Rf groups. It has been considered that in order to develop both water repellency and oil repellency, the orientation of Rf groups on the surface is important, and in order to realize the surface orientation of Rf groups, it is important that the polymer has a melting point attributable to fine crystals derived from Rf groups. For this purpose, an Rf group-containing monomer which forms a homopolymer having a melting point attributable to fine crystals derived from Rf groups (crystallizable Rf group-containing monomer) has been used.
A composition having a copolymer containing polymerized units of such a crystallizable Rf group-containing monomer (hereinafter, referred to also as a crystallizable polymer) as an effective component satisfies the object from the viewpoint of developing water and oil repellency, and improvements have been made in other practical functions. For example, durability against e.g. laundering, dry cleaning and abrasion has been improved by using a monomer which provides high hardness or a monomer having a crosslinkable reactive group in addition to the crystallizable Rf group-containing monomer, or by blending the resulting copolymer with a polymer capable of forming strong coating films.
Further, investigations for softening the hard hand and lowering the melting point of Rf groups in order to develop the water repellency under low-temperature curing conditions, have been made. For example, it is known to copolymerize a monomer containing a perfluoroalkyl group (hereinafter, a perfluoroalkyl group will be referred to as an RF group) having widely ranging chain lengths with an alkyl group-containing monomer.
Further, use of a silicone containing an RF group having widely ranging chain lengths is also known.
For example, a cosmetic composition containing a fluorine type compound and a wax having a specific melting point (for example, Patent Document 1), a quaternary copolymer comprising an RF group-containing (meth)acrylate, stearyl(meth)acrylate and other two types of monomers as essential components (for example, Patent Document 2), a mixture of a fluorine type water and oil repellent with an alcohol containing an RF group having a specific chain length or a perfluoropolyether group-containing alcohol (for example, Patent Document 3), and a reaction product of an amino group-containing silicone and an Rf group-containing ester compound (for example, Patent Document 4) are known. Meanwhile, as an example using an Rf group-containing monomer having a limited chain length, an acryl type heptanary copolymer having RF groups with a specified chain length distribution (for example, Patent Document 5) may be mentioned. It contains at least 40% of crystallizable Rf group-containing monomers. The techniques in this field used in these known art references have improved physical properties from a viewpoint of functions required in addition to water and oil repellency, without impairing the water repellency and oil repellency attributable to Rf groups. However, since an Rf group-containing crystallizable polymer is used as the main component, the following demerits resulting therefrom have not been fundamentally overcome.
Patent Document 1: JP-A-7-173025
Patent Document 2: JP-A-10-237133
Patent Document 3: JP-A-10-81873
Patent Document 4: JP-A-8-109580
Patent Document 5: JP-A-62-179517